With remarkable development of information technology (IT), a great variety of portable information communication devices has been popularized. As a result, in the 21st century, we are moving toward a ubiquitous society in which high-quality information service is possible regardless of time and place.
Lithium secondary batteries are very important to realize such a ubiquitous society. Specifically, lithium secondary batteries, which can be charged and discharged, have been widely used as an energy source for wireless mobile devices. In addition, the lithium secondary batteries have also been used as an energy source for electric vehicles and hybrid electric vehicles, which have been proposed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
As devices, to which the lithium secondary batteries are applicable, are diversified as described above, the lithium secondary batteries have also been diversified such that the lithium secondary batteries can provide powers and capacities suitable for devices to which the lithium secondary batteries are applied. In addition, there is a strong need to reduce the size and weight of the lithium secondary batteries.
Small-sized mobile devices, such as mobile phones, personal digital assistants (PDAs), digital cameras, and laptop computers, use one or several small-sized, lightweight battery cells for each device according to the reduction in size and weight of the corresponding products.
On the other hand, middle or large-sized devices, such as electric bicycles, electric motorcycles, electric vehicles, and hybrid electric vehicles, use a middle or large-sized battery module (middle or large-sized battery pack) having a plurality of battery cells electrically connected with each other because high power and large capacity are necessary for the middle or large-sized devices. Size and weight of a battery module are directly related to a receiving space and power of a corresponding middle or large-sized device. For this reason, manufacturers are trying to manufacture small and lightweight battery modules.
A cylindrical battery cell, a prismatic battery cell, and a pouch-shaped battery cell, which are classified based on their shapes, are used as a unit cell of a battery module or a battery pack. Among these batteries, the pouch-shaped battery cell, which can be stacked with high integration, has high energy density per weight, and is inexpensive, has attracted considerable attention.
A concrete example of the unit cell is shown in FIGS. 1A and 1B, which are exploded perspective views typically showing the general structure of a conventional representative pouch-shaped secondary battery.
Referring to FIG. 1A, a pouch-shaped secondary battery 10 includes an electrode assembly 20 having pluralities of electrode tabs 21 and 22 protruding therefrom, two electrode leads 30 and 31 respectively connected to the electrode tabs 21 and 22, and a battery case 40 to receive the electrode assembly 20 in a sealed state such that portions of the electrode leads 30 and 31 are exposed outward from the battery case 40.
The battery case 40 includes a lower case 42 having a depressed receiving part 41, in which the electrode assembly 20 is located, and an upper case 43 to cover the lower case 42 such that the electrode assembly 20 is sealed in the battery case 40. The upper case 43 and the lower case 42 are connected to each other by thermal bonding in a state in which the electrode assembly 20 is mounted therebetween to form an upper end sealed part 44, side sealed parts 45 and 46, and a lower end sealed part 47.
As shown in FIG. 1A, the upper case 43 and the lower case 42 may be configured as separate members. As shown in FIG. 1B, on the other hand, one end of the upper case 43 may be integrally formed with a corresponding end of the lower case 42 such that the upper case 43 and the lower case 42 may be hingedly connected to each other.
In addition, as shown in FIGS. 1A and 1B, the pouch-shaped battery cell is configured to have a structure in which electrode terminals constituted by the electrode tabs and the electrode leads connected to the electrode tabs are formed at one end of the electrode assembly. Alternatively, a pouch-shaped battery cell configured to have a structure in which electrode terminals are formed at one end and the other end of an electrode assembly may also be manufactured using the above method.